Gate valves are well known and are regularly employed in various industrial and commercial applications. Generally, a gate valve is a valve in which the throttling body, namely the gate or wedge, moves in a linear direction perpendicularly across the substance flow through the valve body. Many critical applications require the valve to reliably operate and provide efficient sealing at high temperatures and under conditions of high pressure and high fluid flow.
It is accordingly known to employ gate valves having flexible wedges for such critical applications. Flexible wedges generally provide a better seal than traditional solid gate valve wedges, as seat face distortions caused by changes in pressure, temperature and external forces can be more easily accommodated by the flexibility of the valve wedge. Flexible wedges also generally reduce pinching and thermal binding of the valve wedge within the seats, which can occur due to large changes in temperature and pressure.
While thermal and pressure induced binding of flexible gate valve wedges occurs less than with solid wedge designs, known flexible wedges have not completely prevented these problems in extreme conditions. Further, the inherent flexibility of known flexible wedges is restricted by their structure, and therefore the amount of seating face distortion which can be accommodated by the gate valve wedge without a loss of sealing ability is limited.
U.S. Pat. Nos. 5,657,961 and 6,338,469, issue respectively Aug. 19, 1997 and Jan. 15, 2002 to Kalsi et al., both describe a flexible wedge gate valve which attempts to overcome these problems. The flexible wedge disclosed comprises a center portion having an internal transverse cavity extending therethrough, which defines flexible walls on both sides thereof. Upstream and downstream pressure boundary plates are integrally connected to the center portion by smaller diameter cylindrical hub sections. Circumferentially extending slots are therefore effectively defined between the upstream and downstream pressure boundary plates and the center disk portion. Accordingly, flexibility of the wedge taught by Kalsi et al. is provided by the transversely extending through cavity and by the outer circumferential grooves. While this structure provides some degree of flexibility, it is achieved by three dimensional bending of the pressure boundary plates around the central disk hub and flexure of the walls surrounding the central cavity, which limits the amount of deflection possible relative to other bending mechanisms which are intrinsically less stiff. The flexibility of the structure disclosed by Kalsi et al. could be increased by making the pressure boundary plates thinner, by reducing the diameter of the of the central disk hub or by making the walls of the central cavity thinner, however these modifications will reduce the strength of the wedge. Further, the deflection of the pressure boundary plates by three dimensional bending causes the seating surfaces thereon to distort, thereby reducing the sealing ability of the gate valve wedge.
Accordingly, there remains a need for an improved flexible gate valve wedge having greater flexibility than known flexible wedges, thereby conferring greater resistance to thermal and pressure induced binding, without sacrificing strength or sealing ability of the gate valve wedge.